1. Field of the Invention
The present invention relates to a scanner and method thereof for scanning images of an original document, for example, film of a camera, by illuminating the document with a light source. In this manner, characters and graphics on the document may be read.
2. Description of the Related Art
Scanners which scan color images of a document are well known in the art. In one such conventional scanner, a lamp is turned on all the time, and a filter with one of three primary colors (red, green and blue) is placed in front of the lamp, thereby radiating light from the lamp onto the document through the filter. Subsequently, light that has passed through the document is received at a photocell, such as a charge coupled device (CCD), and the data thereof is converted from analog to digital, and then stored. By conducting the same operation for each of three color filters, data for the three primary colors is obtained.
Additionally, during scanning for each color, the exposure level is controlled by adjusting, in gradual stages, the levels of analog signals that are generated for the CCD, as well as controlling the accumulation time (exposure time) of the CCD. The exposure level is roughly adjusted by adjusting the levels of the analog signals by stages, while the exposure level is finely adjusted by controlling the accumulation time of the CCD.
In this conventional scanner, as described above, the exposure level is finely tuned by adjusting the accumulation time for the CCD. As a result, accumulation time for the CCD can not be set for a time less than the time required for A/D conversion of the CCD output for storage in memory and, consequently, overexposure may occur.
In order to solve this problem, a darker lamp or an addition of an aperture has been considered. However, by doing so, irregularities in the brightness of the lamp or in the darkness of the filters may appear, thereby varying the brightness of radiation on the original document. Adjustments must be made according to each variance, which is time consuming and inconvenient.
With the above-mentioned conventional scanner, because a filter change is necessary in order to obtain data for each of the three primary colors (red, blue and green), there is an inability to perform quick scanning because of the time required to physically exchange the filters. Furthermore, because the lamp is always turned on, the temperature of the device increases due to heat generation and, as a result, a mechanism to cool the lamp is necessary.
In another conventional scanner, light-emitting diodes (LEDs) for red, green and blue (LEDR, LEDG and LEDB, respectively) are provided to irradiate the document with light from each of the LEDs sequentially. Then the light from LEDR, LEDG or LEDB that has been reflected by the document or transmitted through the document, is detected by a sensor comprising, for example, a CCD and the like.
This second conventional scanner uses a constant current circuit to illuminate each LED and if a large amount of noise is present in the electrical power source, the light emission volume of each LED might fluctuate according to the noise in the electrical power source. With such variation in the light volume of each LED, if images are scanned sequentially, line by line, irregularities occur in the scanned image, causing image deterioration.